While each route of therapeutic drug delivery has its own advantages and limitations, oral delivery is often favored because it offers convenient painless administration, sustained delivery, prolonged shelf life, and often lower manufacturing cost. Its limitations include mucus and epithelial cell barriers in the gastrointestinal (GI) tract that can block access of larger molecules including Therapeutic protein or peptide-based drugs (TPPs), resulting in reduced bioavailability. This review describes these barriers and discusses different strategies used to modify TPPs to enhance their oral bioavailability and/or to increase their absorption. Some seek to stabilize the TTPs to prevent their degradation by proteolytic enzymes in the GI tract by administering them together with protease inhibitors, while others modify TPPs with mucoadhesive polymers like polyethylene glycol (PEG) to allow them to interact with the mucus layer, thereby delaying their clearance. The further barrier provided by the epithelial cell membrane can be overcome by the addition of a cell-penetrating peptide (CPP) and the use of a carrier molecule such as a liposome, microsphere, or nanosphere to transport the TPP-CPP chimera. Enteric coatings have also been used to help TPPs reach the small intestine. Key efficacious TPP formulations that have been approved for clinical use will be discussed.

In this review, our intention was to shed some light on the history of sublingual and buccal delivery over the past 75 years. By searching the query sublingual and buccal, we noticed four steady growth periods in the number of publications between 1950 and 2025. The early phase of sublingual and buccal drug delivery (1950–1982) saw limited attempts to explore this delivery route. The exploratory growth phase (1983–1993) was marked by the use of nitroglycerin to treat angina, calcium channel blockers to treat hypertension, ACE inhibitors to treat heart conditions, the use of opioids in pain management therapy, and peptide and hormonal therapy. The diversification and discovery phase (1994–2009) was marked by the introduction of small molecules for the treatment of opioid use disorder and analgesia, the use of animal models to enhance the pharmacokinetic understanding of the sublingual and buccal route, the use of penetration enhancers, peptide and hormonal therapy, and few marked FDA drug approvals in this area. The innovation and integration phase (2010–2025) was marked by the use of nanoparticles, multilayered mucoadhesive systems, pediatric formulations (fast-dissolving films and tablets), immunotherapy and vaccine delivery, and a broad spectrum of therapeutic agents, such as steroids, antifungals, cannabinoids, antidepressants, antipsychotics, and narcotics (e.g., buprenorphine and apomorphine), novel formulations of fentanyl and diazepam for pain and seizure control, and the introduction of buccal vitamin D3 sprays. Understanding the history of sublingual and buccal delivery demonstrates a growing area of research focused on enhancing mucosal drug delivery for achieving local and systemic therapeutic benefits.

Facial angiofibromas are dermatological manifestations of tuberous sclerosis complex, a neurocutaneous disorder characterized by excess cell growth and proliferation. Oral rapamycin has been used to treat visceral tuberous sclerosis–related tumors; however, the side effect profile of this medicine precludes its routine use in patients lacking significant internal involvement. The authors formulated a novel rapamycin cream that is easy to compound and apply, does not cause local or systemic side effects, and results in a dramatic improvement of facial angiofibromas.

Objective: To mask the bitterness of Chlorpheniramine Maleate via encapsulating drug into Eudragit EPO microparticles, and then incorporate these microparticles into orally disintegrating films (ODF) and orally disintegrating tablets (ODT) for pediatric uses. Methods: Spray drying of water-in-oil emulsion was utilized to encapsulate Chlorpheniramine Maleate into Eudragit EPO microparticles. Based on an orthogonal experimental design L₉ (3³), polynomial regression models were developed to evaluate correlation between microparticle properties (encapsulation efficiency and drug release) and variables (X₁: weight ratio of polymer to drug, X₂: volume ratio of oil to water and X₃: Q-flow of spray dryer). ODF and ODT formulations were evaluated including weight variation, content uniformity, tensile strength, disintegration time, friability and dissolution profiles. The bitterness taste test was evaluated in 10 adult volunteers. Results and discussion: From polynomial regression analysis, the best values of variables leading to the optimized microparticles were X₁ = 10, X₂ = 3 and X₃ = 45. The optimized microparticles were incorporated into ODF and ODT with satisfactory weight and drug content uniformity, and acceptable physical strength. Both dosage forms disintegrated immediately (less than 40 s) in simulated saliva solutions. The outcome of taste-masking test indicated that microparticles alleviated drug bitterness significantly; bitterness was not discernible with microparticles incorporated in ODT, whereas only slight bitterness was detected from microparticles incorporated into ODF. Conclusion: Both ODF and ODT are shown to be suitable vehicles for taste masked Chlorpheniramine Maleate microparticles with potential for pediatric uses.